Instructions For StrombergNA.R6G AIRCRAFT CARBURETORS

MAIN METERING SYSTEM: Air passing up-ward through the Venturi (21) at high velocityproduces a reduction in pressure (a suction) on themain discharge nozzle (22), This causes fuel fromthe float chamber to be drawn through the mixturecontiol needle seat (10), then through the mainmetering jet (9), and into the fuel channel (16). TheVenturi vacuum (suction) also draws air throughthe main air bleed (25), Thus a small amount of airmixes with the fuel in ihe main discharge nozzle (22).This fuel and air is discharged into the air passingupward through the Venturi (21) and forms thecombustible charge for the engine. The throttlevalve (18) regulates the quantity of this mixturepassing to the engine, thus regulating the poweroutput. This main metering system is used for allengine operating conditions except idling.

ECONOMIZER SYSTEM: To provide a richmixture at wide open throttle, which is necessaryto obtain maximum power and to prevent overheat-ing of the engine, an additional fuel passage isopened by a valve known as the economizer. As thethrottle is opened beyond a certbin point, the econe-mizer arm (27), mounted on the pump stem andactuated by the throttle lever (17), opens theeconomizer valve (8). When the economizer valve(8) is open, the rate of firel flow through the econo-ryizer system is regulated by the economizer meter-ing jet (7). The fuel flowing through this jet joinsthe fuel from the main metering jet (9) to providethe rich mixture.

As the throttle valve is closed, the economizervalve spring (26) closes the economizer valve (8),

GENERAL DESCRIPTION OF THE NA.R6GCARBURETOR

The Stromberg Model NA-ROG Carburetor is aqingle barrel, updraft unit. It has a single hinge typefloat mechanism, a metering needle -tvpe riixtuiecontrol and Idle Cut-ofr, a tf,rottle actuited econo-mizer valve, a. throttle ictuated accelerat'lg pumpand an idle mixture adjustment quadrant. -

The NA-R6G Carburetor was designed to giver-"aximum maneuverability, with a flo-at type car-buretol for use on aircraft 6ngines of approiimately220IJP.

- Iltq bar_rel size is #6, -the actual diameter being2-7 116 inches. This proi'ides for the use of a maxilmum Venturi size of Z-f 7f O inches.

The specifications and settings in this carburetorare the result of a great deal oflest work conducted.by lhe-engine and carburetor manufacturers, bothin the laboratory and in flight, and should riot bechanged unless it is obsolutely c'ertain that a changeis necessary to meet unusuai operating conditiofr.

FUNCTIONING OF CARBURETOR

. This carburetor operates on the same basic prin-ciples used in q-t!-ei Stromberg models. Refeiringto tr'igure 2, it will be noted thal fuel enters the car]buretor through the fuel inlet (l), pa,sses downwardand t.hrgugh the Fuel Strainer Assembly (2), andenterd the float chamber after passing throirlh the.float-needle valve (3). The float needle valve (B)and float (4) maintain a constant level of fuel in th6float chamber.Form 10.O26Jure 21, l9(l Page One

STROMBERG NA.R6G AIRCRAFT CARBURETOR

DUST COYERASSEMBLY

IDI."E MXTUREAII,USTMENT

THROTTLE STOP

.I/AIN AIR BLEED

THROTTL"E VALVE

IDLE SPEED ADJUSTMENT

MANUAL MIXTURE CONIROLL"EVER

THROTTI.T LEVER

FUEL INLET

Figure I

Copyright 1943Beadir Aviatiou Corpontion

South Bcad, Indiam

Page Two

stopping the flow of fuel through the economizermetering jet (7). This. makes available a leanermixture, which in turn makes possible a considerablefuel saving for part throttle engine operation.

MIXTURE CONTROL: It is a well known factthat the mixture ratio delivered by the carburetorwill become richer as an airplane climbs, due to de-creased density of the air. To compensate for thisenrichment when flying at various altitudes, a mix-ture control valve has been provided which is.oper-ated independently of the throttle.

As the mixture control lever (6) (shown in fullrich position) is moved to the right, the mixturecontrol needle (5) is moved downward into the mix-ture control valve seat (10) by the eccentric pinwhich is a part of the mixture control shaft. Thisreduces the flow of fuel, and makes possible an ad-justment of the mixture ratio at any altitude.

ACCELERATING PUMP: To enable the engineto accelerate quickly and smoothly, o pump is util-ized to provide additional fuel as the throttle valve(f8) is opened. The pump sleeve (12) moves downas the throttle opens, and produces & pressure onthe fuel within the sleeve. This pressure produces adownward force on the pump piston (13) whichexceeds the force of the pump spring (15) and pushesthe pump piston (13) down. This uncovers the holesin pump valve (14) allowing the fuel above thepump piston (13) to pa,ss downward through thepump valve and to the main discharge nozzle (22).The pump spring (15) gradually forces the pumppiston (13) up, producing a delayed fuel dischargeuntil the piston seats on the valve which stops theflow from the pump. As the throttle valve (18) isclosed, the sleeve is raised and the chamber withinthe sleeve is filled with fuel, which flows around theoutside of the piston from the float ehamber.

IDLE SYSTEM: When the engine is idling thethrottle valve (18) is nearly closed, so the flow ofair lhlqugh the Venturi (21) is insufficient to produceenough v&cuum (suction) to draw fuel from themain discharge nozzle (22). A separate idle systemhas, therefore, been incorporated to give the neces-sary fuel flow at low engine speeds. This systemutilizes the high v&cuum (suction) which existsabove the throttle valve (18) to draw the fuel froma nozzle during the idling condition. This system isshown in Figure 3.

Fuel from ttre float chamber first passes throughthe main metering jet (9) to the main dischargenozzle (22), and flows through side holes in the maindischarge nozzle. It then enters the idle meteringtube (24) and mixes with a small amount of airfrom the idle air bleed (23). This fuel and, air emul-sion is drawn into the carburetor barrel through theidle dischargenozzle (19) by the high vacuum (suc-tion) which exists above the throttle valve. Afterleaving the idle discharge nozzle, the fuel and airis mixed with more air which p&sses the nearly closedthrottle valve giving a correct mixture for idling.As the throttle valve is opened, the vacuum (suction)at the idle discharge nozzle decreases and the v&cuum(suction) at the main discharge nozzle increases sothat the fuel ceases to flow through the idle system.It then flows through the main system.

INSTALIATIONThe carburetor should be so mounted on the engine

that the float chamber is at the side of the throttlebarrel, preferably with the fuel inlet to the rear ofthe engine. With the carburetor in this position, thethrottli lever, adjustable radially in 15o increments,will be on thi left side and the mixture control leveron the right side, as viewed from the rear of 'theengrne.

The fuel inlet is a 5 /8o pipe tap connection locatedin the upper rear pait o.f itte riaitt body. If a fuelpump is-rised, a piessure of 3 lbs. per square inchit tlre carbuietoi is recommended and provisionshould be made for a fuel pressure gauge connectionnear the carburetor. If a giavity feed system is used,the tanks should be so locateil that the minimumhead of fuel on the carburetor inlet is 24'under allnormal conditions of flight.

STARTINGThe probedure for starting recommended by the

engine -manufacturer

should-be followed closely.- Ifa primer is provided, it should be used when startinga iold engiie. The eiact procedure in starting varieswiin tne type of startin! equipment on the engine,but at low-cianking speel, fuel can be drawn out ofthe idle system piooiaea'the throttle is closed orver$ nearly closed during the cranking operation.As ioon ai the engine starts to fire, it is usuallynecessary to open the throttle slightly to keep ttreengine runninf and to warm it up sufficiently fornormal operation.

During cold weather when a very rich mixture isrequiredlor warming up, the engine may be keptrunning by partially ope-ning the throttle frequentlyto givelhil engine an accelerating charge of fuel.

WARNING: Do not operate the titrottln before theengine stwts to rtre, The fuel thus puttlpgd lrom tlwu,ibwetor will settle in the uir intnlw and there is apossibilitg of its catclving f're i! th.e engine baclcfireswhm it stnrts,

ADJUSTMENTThe main and economizer metering iets used in

this carburetor are of the fixed orifice t;pe, so noadjustment for cruising and full throttle speeds isrequired. An idle adjuitment is provided -to takecarre of slight production variations in the carburetorsand enginis. A small lever at the front of the throttlevalve Sody may be moved to control the richnessof the mixture at idling speeds. A quadrant behindthis lever indicates by the letters R and L the direc-tion to move the lever to obtain a rich or lean mix-ture and also acts as a locking device to hold thelever in position. A throttle stop adjusting, screw isprovided on the throttle shaft, which should be ad-justed to obtain the desired engine idling speed.Both the throttle stop and the idle adjustmentshould be set with the engrne at normal operatingtemperatures to obtain the proper idling speedand smooth operation.

SERVICINGOnce the carburetor has been properly installed

and the idle adjustments made, very little attentionis required in service. A fuel strainer (2), Figure 2,

Page Thrce

l00cot:doE

FUEL INLETFUEL STRAINER ASSEMBLYFLOAT NEEDLE VALVEFLOATMIXTURE CONTROLNEEDLEMIXTURE CONTROLLEVE

) ECONOMIZER METERING JET(8) ECONOMIZER VALVE(9) MAIN METERING IJET(|O) MIXTURE CONTROL NEEDLE SEAT(II)FLOAT NEEDLE VALVE SEAT

e6) ECONOMIZER VALVE S,PRING

7l ECONOMIZER ARM

ACGELERATING PUMPPUMP SLEEVEPUMP PISTONPUMP VALVEPUMP SPRING

il7)(t8)fl9)eo)

(2I) VENTURI

MAIN DISCHARGENOZZLE

(23) IDLE AIR BLEED(24) IDLE METERING

TUBE(25) MAIN AIR BLEED

DIRECTION OFAIR FLOYY

THROTTLE LEVERTHROTTLE VALVEIDLE DISCHARGE NOZIDLE MIXTUREADJUSTING

16) FUEL CHANNEL

FULL THROTTLE

FIGI'RE 2

SOHEMATIC DIAGRAM OF NA-R6G GARBURETOR

IDLING

FIGURE

I't'ltr;l;

illllrtl\,rrli

I

)::

is located in the chamber, under the fuel inlet of thecarburetor. The fuel strainer assembly should beremoved frequently for cleaning. This may be doneby removinf the- square head strainer assemblyplw, usiDg A-24563 square socket. After remo-val,iin6 tle "streiner ass'embly thoroughly in clearigasoline being sure that all.dirt that may haveeettled into ihe sump of the strainer assemblyplug has been stirred up and removed.

DUST COVER-A leather dust cover assemblycovers the accelerating pump operating mechanism.This cover &nswers a-two-fold purpose, l-to keepdust and dirt away from the operating mechanismand 2-to mainta,in a small a'mount of lubricanton these parts. When t"his cover is replaced afterremoval for inspection, cleaning or overhaul, a-verysmall amount of lubricating grease should be placedon the pump stem and fork assembly.

CAUTION-Do not fill the dust cover withgrea,se as the parts it is protecting requireonly a very small amount of lubricant.

The carburetor should be inspected frequently tosee that all parts are tight and properly safetied.

OVERHAUL OF NA.R6G CARBURETORAt each regular engine overhaul period, the car-

buretor should be disassembled for cleaning andinspection. This must be done in a clean place,with the necessery tools, which are listed at the endof these instructions. If these tools are not available,the carburetor should be taken to a dependablerepair shop having the necessary overhaul equip-ment and trained pprsonnel.

DISASSEMBLY: AJter the carburetor has beenremoved from the engine and cleaned on the outside,the halves of the carburetor may be separated bythe removal of the six fillister head screws at theparting surface.

The mixture control needle and the pump sleeveare held in the upper half or throttle valve body,and wilt be drawn out of the lower haU or main bodyas the throttle body is lifted ofr. The Venturi is heldin the main body by a hexagon head screw.

The pump sleeve is a brass stamping and easilydamaged. To prevent any danger of its droppingon the floor or bench, it should be slipped ofr theoperating s6s6 immsdiately.

To prevent damage to the carburetor, it is veryimportant that the correct tools be used for removingeach part. A list of parts and the special wrenchesto be used for their removal follows:

AII variable parts should be checked to see thattheir sizes are in accordance with the carburetorspecification sheet.

To check the float for leakage, submerge the floatin hot water &pproximately 8r.22'C. (180' F.) andwatch for leaks-. In case

-of leaks in the float, it

should be dried out so no fuel or water remains in-side; then, it should be soldered. Care should betaken in oider that no larqe amount of solder i8 lefton the float which would increase the weight andchange the fuel level. After soldering, the floatshoui'd be neutralized to eliminate any corrosiveaction which might be caused by soldering acid.

The float needle valve and eeat should be checkedfor leakace bv holdine the needle valve with thepoint up in'd ieat in plice and filling the slnsll spaceibove ihe needle wiih gasoline. Ii any leakage isevident, the needle should be lapped into the seatwith coicus powder or very fine giinding,compound-If leakage cdnnot be stopped, a new needle and geat

should 5e used. as it ii verv aifficult to fit & newneedle to an olci seat or a nei seat to an old needle

REPLACEMENTS: When ordering parts it isnecess&rv to sive complete information concerningthe part's desiied to av^oid delay in sliFmeqt or thereceipt of wrong parts. Wherever possible the serialnumber of the c-aiburetor should b-e given. A carefulreference to the attached a,ssembly drawing #3952L5should be made to determine the conect part num-ber. If the part number is marked with an asterisk(*), the paft is a variable part end the correct eizedUiiuld be given as specified

-on the specification nheet.

The number for the complete set of gaskets forthis carburetor model is indicated on the assemblydrawing.

REASSEMBLY: All headless screw plugs belowthe fuel level should be assembled with shellac. Careshould be taken not to cet shellac on the ends of theplugs where it may coie ofr and be carried by theiuefinto one of thi metering orif.ces' Eeadless screwnluss above the fuel level-and all other threadedbat{s sctewed into the bodies should have a com-

iound of graphite and caster oil prt on-the-tbireads.i,ockwireill parts provided with lockwire holes.

FUEL LEYEL: Flost chamber fuel levele areset at the factory to conform. with specification Bheeton ttl-n6c Cdrburetors with a fiel pressure of 3pounds per squere inch, and with a fuel of 0.710 spe-cific gravity.

NOTE : I pound per square i'lch of pr-essureis equal to a gr&ilty Lead of 39 inches of0.710 specific gravity fuel.

To check the float chamber firel level, reler tospecification sheet under "Float Mechanism"- Thecleck should be made using the e&me fuel pressureand fuel which are regularly rised in service.

F\rel level adjustment is made by remoqg lhefloat valve seai and changing gaskets' Thickergaskets lower the level and tlinnei gaskets-raise it.One sixty-fourth inch change in gasket thjcloesswill charige the level appro=ximately-5i64'. Afterassembhn! the needle seat, needle valve and float,the float Jhould be moved irp and down to see thetit works freely on the fulcruin screw and the needleworks freely in its seat.

Page Ftve

Part Name Tool NumberFloat Needle Seat T-19276Guide, Mixture Control Needle T-L9272Mixture Control Seat T-20199Economizer Assembly T-19278Metering Jets T-24923

INSPECTION AND CLEANING: The bodiesand all parts should be thoroughly cleaned in gaso-line and all passages blown out with compressed air.Parts which should be inspected for wear are: floatassembly, pump unit, mixture control unit, throttleehaft and bushings.

ECONOMIZER SETTING: The economizerset-ting is the angular travel in degrees of ttre throttlevalie from the fully closed position to the positionat which the economizer starts to open.

Example: If the specification specifies an 18"throttle 'valve angle under "Idle System" and asetting of 45" undei "Economizet"r_the3 the throttlevalve position, measured from the horizontal top orattaching flange surface, should be 63" when theeconomizer starts to travel.

This setting is obtained by clamping the pumplever on the trhrottle shaft with the throttle in thecompletely closed position (idle speed adjusting screwbacEed ofi) and the center of the pump lever pin15132'below the top flange of the carburetor asshown in Figure 4. The pump lever and throttleshaft should then be pinned together as indicatedin Figure 4. The economizer setting should then bechecked by measuring the angle of the throttlevalve when the economizer &rm contacts the econo-mizer valve. The point at which the economizervalve starts to open can be felt when the throttle isopened slowly. Small adjustments may be made bycarefully bending the economizer &rm (27), Figure 2.

MIXTURE CONTROL: When any parts of themixture control system are replaced, care should betaken to see that they are assembled correctly.

The mixture control needle is operated by aneccentric pin which is a part of the mixture controlstem assembly. It is important that the stop on thestem be located at the correct angle with respectto the eccentric pin. This may be accomplished by

pinning the stop on the stem so that the eccentriciin is f,oward the pump mechanism and the bottomof tnis eccentric pin is 25/32'from the parting sur-face, and the stop is against the stop screw iu thefull rich position as shown in Figure 5.- The mixture control^needle should be screwedinto the needle holder-and adjusted to conformwith the travel given on the specification sheetunder "Mixture Clntrol Needle". This travel is tobe obtained when the mixture control lever movesfrom the fully closed position to the fully open posi-tion. The lever should travel 75 to 80 degrees asindicated in Figure 5.

An approximate adjustment may be obtainedbefore asiembling the needle valve in the throttlebody by settinglhe bottom of the needle holderslot- 17-132" from the main body parting surfacewith thi needle valve held down against the needlevalve seat (See Figure 6). When f[iq preliminaryadjustment has been made, assemble the two halvesof'the carburetor together and determine if theneedle has the specified travel.

The needle travel may be checked by removingthe plug and jet below the needle and using thesimpie apparatus shown in Figure 7. When in thefull lean jiosition, the needle stops against the needlevalve seat; when in the full rich position, .the stopstrikes the stop lug. When the proper adjustmenthas been madd, pin solder the needle as shown inFigure 6 to prevent its changing in Service. In assem-bling the ndedle in the carburetor throttle body, theslot-in the needle holder should be placed with theopening facing the pump mechanism.

Tool No.T-19279T-24950T-16910T-19492T-18170T-18172T-24923T-19272T-20199T-19278T-24944T-24963T-20183T-20184T-L9276

i-zozzzT-24957

NA-R6G OVERHAUL TOOISName

Handle, Sliding Offset.Handle, Metering Jet Screw Driver.Reamer, Throttle Bushing.Remover, Throttle Bushing.ScrewDriver......ScrewDriver.....Screw Driver, Tlpe A & B Metering Jet.. . .

Socket Screw Driver. . . . .

Socket Screw Driver, Mixt. Cont. SeatSocket Screw Driver, Econ. Assy.. .

Socket, DoubleHex... .......Socket, Square.tT" Wrench Extension.

Handle Bar (for use with T-20183).Socket, Screw Driver End.

Wrench, End...Taper Pin Reamer (with handle). . . . .

Size318" x8o

.4395 Dia. x 15 5/8"

.037 x 3 /8'

.047 x I 14'

.062" x.687"

.048il x.547il

.062'x.547ne 116'11 /16' Sq.5" with'3 /8' Driver7n

.068" x 3/4'with

.484" Pilot for Float Seat314" xL3lL6'-L18'For #0000 Taper Pin

STROMBERG AIRCRAFT CARBURETOR SERVICEBcndix Productr Divieion

South Bcnd, Indianau. s. A.

Page Six

ADJUSTMENT OF PUMP LEVERON THROTTLE SHAFT

ASSEMBLE PUMP LEVER TOJ5/32,' DIMENSION WITH THROTTLEVALVE COMPLETELY OLOSED(IDLE SOREW BAOKED OFF)

*+z (.ogssionru rHRUREAM ront+oooo rApERPIN AND ASSEMBLE P14577PIN AFTER AD.JUSTING

++z (.ogss) DRrLL THRUASSEMBLE PIN P-9182AND RIVET IN PLACE

ULL CLOSEDOR IDLE OUT.OFF FOSITION

__EAEM!G suEFAcE t__-.FIG.5

I

3/32 DrA. ROD

R AFTER tlto':-zq'rnREADsADJUSTING *r

4l(.os€) DRTLLTHRU

PERL I MINARY ADJUSTMENTOF MIXTURE CONTROL

NEE DLE

TOOL FOR CHECKII{GMIXTURE CONTROL

NEEDLE TRAVEL

FULL RICH

FIG.6 FIG.7

Page Seven

392522 (r/8 PrPE)F6869(2-REP.

x 3900t5

P-6666 COTTER i(Ft393r0DLE T

670(o-32)P-t6708 75P-t3657 P-r3905

P-t38753834 I I

P.13952

*P-2180

390060 ,d FUEL LEVEL*3902s9

P-6564 |/32 P-t86023 8 3565P-3t99P-5668P-t3898

*P-t3960Fil640 (3,/8

P-il430 P-13963(r./64 THTCK)

P-t3964(3/64 THTCK)P-r3965(t/r6 THTCK)39O256--=-

36

P-r r582(9/r6-24) SECTION A-A

P-t9086 390090383350383352 (9-RE0.)P-6670(rO-32)P-r629 9

39021938380t (3-REO)

P-658r

6563

P-1659 r250390006 3902 396r F9187P-8576 (6 REO.) r3942 P-13962

P-r3940P-t5344(6 REQ.)

P-8460(5/t6'fP-6O166(MA|N ArR BL

Ft6630(2- P-r3688 P-l|72639 P-10666(r/32 THrCK)

F60307(r/64 THrCK)

F60308(3r'64 THrCK)

P-il582 (9/t6-24)

P'r80r2

P-8sO8 fl

P-\6r(7/t6-24)174-S-22

P-toz4eF/8-24',,P-60il7 (4- P-8460(5/r6-2P-6O3t2(8-RE P-8508fi/8 PtPE)

390224

'(39OI88 ECON- METERING JET

SECTION D-D-D-D 20(7/t6-24' SECTION E-E P-2886 SECTION F-F390249 MAIN BODY P-t3620(7/tti-24,*39OI88 MAIN I'ETERING JET

Mtrc-corPLEm 3ET OF 6A3XEr3 fOR CnllJeElOR,39C283

SECTION B-BP-9008(t/4 PtPE)

SECTION C-C

BENDIX PRODUCTS DIVISION, SOUTH BEND,INDIANA, U.S.A.

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